One of the most highly regarded reasons for breastfeeding is to convey the mother's immunity to common germs and diseases to the newborn via her milk. The immune system of a newborn baby is in its own kind of infancy since it's been protected in the womb from exposure to environmental pathogens. A recent study suggests a degree of immunity might also be conveyed to the baby at the time of its conception.

Kai Willführ, of the Max Planck Institute for Demographic Research in Rostock, Germany, and Mikko Myrskylä, of the London School of Economics and Political Science in the United Kingdom, went 300 years back in time to the St. Lawrence Valley in Québec, Canada, to see if there was a connection between disease load at conception and the child's health in later years.

Disease load at conception refers to the state of health of the child's parents as well as to the surrounding environment. The researchers picked this time and place because of well-documented population records and a series of epidemics that occurred during the typical lifespan of someone at that location between 1705 and 1740.

Between 1705 and 1724, there were 28,035 children born in the Canadian valley. That number of children was narrowed down to just those born to women and their husbands married for the first time; first marriages eliminated any negative health effects of being a stepchild or orphan.

The number was further narrowed to just the children in families where one child was conceived in 1714 or 1715, during a measles epidemic. The researchers wanted to compare mortality rates between siblings conceived before and after the epidemic to those conceived during it. Also eliminated were children of parents whose birth and death dates or residential status were missing.

After all eliminations, the study encompassed 575 families of 7,947 children.

The death rate (mortality) in the valley was divided into these segments:


  • 1705 to 1714: a Stable rate of mortality
  • 1714 to 1715: a Severe epidemic of measles, killing many infants and toddlers
  • 1715 to 1729: Stable mortality rate
  • 1729: High mortality rate due to the unidentified crisis that might have been a measles epidemic or famine due to crop failures1729 to 1734 — smallpox epidemic killed many people, especially those younger than 30
  • 1734 to 1740: Mortality rates stabilized

Children conceived during the 1714-1715 measles epidemic were more likely to survive the double crisis of 1729-1734 than their siblings conceived before or after it. They were, however, more prone to die from other causes before and after the 1729-1734 crisis.

Source: Willführ, Kai, and Mikko Myrskylä. "Disease Load at Conception Predicts Survival in Later Epidemics in a Historical French-Canadian Cohort, Suggesting Functional Trans-Generational Effects in Humans." PLOS One. PLOS. Apr 16, 2014. Web. Apr 30, 2014.